Device for mixing two flows of fluid which are initially guided separate from one another in a bypass jet engine

ABSTRACT

The invention relates to a device for mixing two fluid flows, initially guided separately from one another, in a two-circuit reaction engine, a mixing tube which encloses a hot core stream being provided, along the outer shaped lateral surface of which a cold bypass flow flows. The mixing tube is designed in the form of a truncated cone narrowing in the direction of flow and has openings arranged at the downstream end in the circumferential direction of the mixing-tube lateral surface in a cross-sectional plane lying perpendicularly to the longitudinal axis of the mixing tube. The hot core stream flowing through the mixing tube penetrates through the openings into the cold bypass flow flowing around the mixing-tube lateral surface. The openings have passage areas of elliptical shape with a major axis and a minor axis, the major axis of the passage areas running on the lateral surface of the mixing tube in the direction of flow of the fluids and the minor axis running perpendicularly thereto.

BACKGROUND AND SUMMARY OF THE INVENTION

Device for mixing two flows of fluid, which are initially guidedseparate from one another, in a bypass jet engine

The invention relates to a device for mixing two fluid flows, which areinitially guided separately from one another, in a bypass jet engine.

To this end, it is known that “lobe mixers” are used in bypass jetengines in order to mix the hot core stream of the jet engine and thecold bypass flow before discharge from the jet engine nozzle. In thiscase, the hot core stream of the jet engine is guided through a “mixingtube”, whereas the cold bypass flow flows along the outside of themixing-tube lateral surface. The mixing of the two fluid flows is forcedby the special shaping of the downstream lateral surface of the mixingtube. For this purpose, that lateral surface of the mixing tube which isformed downstream has “lobes” which extend radially outward. In thiscase, after flow has taken place through or respectively around thedownstream section of the mixing tube, these lobes direct said hot corestream into the cold bypass flow, and also direct the cold bypass flowinto the hot core stream. With regard to the known prior art, referenceis made, for example, to GB 2 160 265 A.

A disadvantage with these known lobe mixers is in this case the factthat the lobe mixers, on account of the large radial extent of the lobesat the downstream end, tend to vibrate and in addition deformationsoccur due to material heating and pressure differences. It has thereforebeen attempted to remove these disadvantages by “struts” which supportthe lobe mixer on the outlet cone or the nozzle housing of the reactionengine. However, these struts constitute an additional source of weight.

In addition, on account of the large radial extent of the lobes of thelobe mixer, interference may occur in the region of the enginesuspension between the lobes of the lobe mixer and the enginesuspension. To avoid such interference, the relevant lobes of the lobemixer, the “pylon lobes”, are designed differently. However, this hasthe disadvantage that a decrease in the mixing efficiency is associatedwith the redesign of the “pylon lobes”.

The object of the invention is to provide a remedy here by a new designof the device for mixing the hot core stream of the reaction engine withthe cold bypass flow.

Based on a device of the type mentioned at the beginning, this object isachieved according to the invention in that the mixing tube is designedin the form of a truncated cone narrowing in the direction of flow ofcore stream and bypass flow, and in that the mixing tube has openingsarranged at the downstream end in the circumferential direction of themixing-tube lateral surface in a cross-sectional plane lyingperpendicularly to the longitudinal axis of the mixing tube, throughwhich openings the hot core stream flowing through the mixing tubepenetrates into the cold bypass flow flowing around the mixing-tubelateral surface.

The mixing tube design according to the invention leads to substantialadvantages. By the openings being provided in the mixing-tube lateralsurface, lobe mixers with the large radial extent of their lobes aredispensed with. The vibration tendency is thus substantially reduced, sothat the hitherto requisite struts are dispensed with. The risk ofpossible interference with the engine suspension thus does not ariseeither. In addition, the smaller radial extent has the advantage thatthe novel mixing tube according to the invention is also suitable forconfined installations.

Furthermore, the closed annular lateral surface at the downstream end ofthe mixing tube leads to a robust, low-vibration construction, so thatdisturbances on account of fluctuations in operating pressure andtemperature have less effect on the mixing tube. Since supporting strutsare no longer necessary for fixing the mixing tube, this omission of thesupporting struts at the same time also entails a lighter constructionand thus lower weight of the reaction engine.

Furthermore, the simplified form of the mixing tube leads to a morecost-effective production, since the complicated deep-drawing operationsrequired for producing the lobes are dispensed with.

According to a further feature of the invention, the openings in themixing-tube lateral surface have passage areas of elliptical shape witha major axis and a minor axis. In this case, the major axis of theelliptical passage areas runs on the mixing-tube lateral surface in thedirection of flow of the hot core stream and of the cold bypass flow,and the minor axis is arranged perpendicularly thereto.

Further features of the invention follow from the subclaims.

A combination of the novel mixing tube according to the invention withsufficiently well-known conventional lobe mixers is possible. Thereplacement of existing mixers with mixers according to the invention isconceivable, since the changes of the new mixer regarding mixerefficiency (lower) and overall pressure loss (lower) act in a neutralmanner with regard to the gain in thrust.

The invention is described below with reference to an exemplaryembodiment shown more or less schematically in the drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a sectional representation of a mixing tube of atwo-circuit reaction engine in the form of a truncated cone withopenings distributed over the circumference of the truncated cone, and

FIG. 2 shows an enlarged representation of an opening from FIG. 1.

DETAILED DESCRIPTION OF THE DRAWINGS

A mixing tube designated overall by the reference numeral 10 in FIG. 1and intended for mixing two fluid flows, initially guided separatelyfrom one another, in a two-circuit reaction engine comprises a lateralsurface 12 and a longitudinal axis 14. The direction of flow of thefluid flows to be mixed, that is to say of a hot core stream 16 and of acold bypass flow 18, is indicated by the arrows S.

In this case, the mixing tube 10 is in the form of a truncated conenarrowing in the direction of flow S. The other components of a reactionengine, apart from the mixing tube 10, are not shown for reasons ofclarity.

At the downstream end of the mixing tube 10, a plurality of openings 20are incorporated in the mixing-tube lateral surface 12 in thecircumferential direction of the mixing-tube lateral surface 12 in across-sectional area lying perpendicularly to the longitudinal axis 14of the mixing tube 10.

An enlarged representation of one of the openings 20 lying at thedownstream end of the mixing tube 10 is shown in FIG. 2.

In this case, the openings 20 have a passage area 22 of elliptical shapewith a major axis 24 and a minor axis 26. Whereas the major axis 24 ofthe passage areas 22 runs on the mixing-tube lateral surface 12 in thedirection of flow S, the minor axis 26 is arranged perpendicularlythereto.

In addition, the elliptical passage areas 22 have a hole collar 28 onthe outside of the mixing-tube lateral surface 12.

As FIG. 2 shows, the height of the hole collar 28 is designed in such away that the maximum height of the hole collar 28 is located at theupstream apex 30 of the major axis 24 of the elliptical passage areas 22and decreases from there in the direction of flow S. A region of thedownstream apex 32 of the major axis 24 of the elliptical passage areas22 is formed without a hole collar 28. It may alternatively be bentinward (relative to the mixing-tube lateral surface 12).

In the present exemplary embodiment, the transition from the outside ofthe mixing-tube lateral surface 12 to the hole collar 28 is of concavedesign; other continuous configurations are also possible.

The mode of operation of the device described above is as follows:

Whereas the hot core stream 16 coming from the reaction engine flowsthrough the conical mixing tube 10, the cold bypass flow 18 flows aroundthe mixing-tube lateral surface 12. The hot core stream 16 flowingthrough the mixing tube 10 penetrates through the openings 20 at thedownstream end of the mixing tube 10 into the cold bypass flow 18flowing around the mixing-tube lateral surface 12. As a result of thedesign of the passage area 22 and of the hole collar 28, goodintermixing of the two fluid flows is achieved with low pressure losses,this intermixing corresponding to the greatest possible extent to thatof the known lobe mixers.

1. A mixing tube for enclosing and guiding a hot core stream of a jetengine, said mixing tube having a lateral wall with a laterally outwardfacing surface over which a cold bypass flow flows and a laterallyinward facing surface over which the hot core stream flows; wherein saidmixing tube is configured as a truncated cone which narrows in adirection of flow through the mixing tube; wherein mixing openingsextend laterally through said lateral wall of the mixing tube at itsdownstream end to accommodate flow therethrough of portions of the hotcore stream which then penetrates into the cold bypass flow along theoutward facing surface; wherein the openings have a passage area ofelliptical shape with a major axis and a minor axis; and wherein themajor axis of the passage area runs on the lateral wall of the mixingtube in the direction of flow and the minor axis of the passage arearuns perpendicularly thereto.
 2. A mixing tube for enclosing and guidinga hot core stream of a jet engine, said mixing tube having a lateralwall with a laterally outward facing surface over which a cold bypassflow flows and a laterally inward facing surface over which the hot corestream flows; wherein said mixing tube is configured as a truncated conewhich narrows in a direction of flow through the mixing tube; whereinmixing openings extend laterally through said lateral wall of the mixingtube at its downstream end to accommodate flow therethrough of portionsof the hot core stream which then penetrates into the cold bypass flowalong the outward facing surface; wherein the openings have a passagearea of elliptical shape with a major axis and a minor axis; and whereinthe passage area has a hole collar on the laterally outward facingsurface of the lateral wall of the mixing tube.
 3. A mixing tubeaccording to claim 2, wherein a transition from the laterally outwardfacing surface of the lateral wall of the mixing tube to the hole collarof the passage area is of concave design.
 4. A mixing tube according toclaim 2, wherein a height of the hole collar with respect to thelaterally outward facing surface of the lateral wall of the mixing tubevaries in such a way that a maximum height of the hole collar is locatedat an upstream apex of the major axis of the elliptical passage area anddecreases from there in the direction of flow.
 5. A jet enginecomprising a mixing tube for enclosing and guiding a hot core stream ofthe jet engine, said mixing tube having a lateral wall with a laterallyoutward facing surface over which a cold bypass flow flows and alaterally inward facing surface over which the hot core stream flows;wherein said mixing tube is configured as a truncated cone which narrowsin a direction of flow through the mixing tube; wherein mixing openingsextend laterally through said lateral wall of the mixing tube at itsdownstream end to accommodate flow therethrough of portions of the hotcore stream which then penetrates into the cold bypass flow along theoutward facing surface; wherein the openings have a passage area ofelliptical shape with a major axis and a minor axis; and wherein themajor axis of the passage area runs on the lateral wall of the mixingtube in the direction of flow and the minor axis of the passage arearuns perpendicularly thereto.
 6. A jet engine comprising a mixing tubefor enclosing and guiding a hot core stream of the jet engine, saidmixing tube having a lateral wall with a laterally outward facingsurface over which a cold bypass flow flows and a laterally inwardfacing surface over which the hot core stream flows; wherein said mixingtube is configured as a truncated cone which narrows in a direction offlow through the mixing tube; wherein mixing openings extend laterallythrough said lateral wall of the mixing tube at its downstream end toaccommodate flow therethrough of portions of the hot core stream whichthen penetrates into the cold bypass flow along the outward facingsurface; wherein the openings have a passage area of elliptical shapewith a major axis and a minor axis; and wherein the passage area has ahole collar on the laterally outward facing surface of the lateral wallof the mixing tube.
 7. A jet engine according to claim 6, wherein atransition from the laterally outward facing surface of the lateral wallof the mixing tube to the hole collar of the passage area is of concavedesign.
 8. A jet engine according to claim 6, wherein a height of thehole collar with respect to the laterally outward facing surface of thelateral wall of the mixing tube varies in such a way that a maximumheight of the hole collar is located at an upstream apex of the majoraxis of the elliptical passage area and decreases from there in thedirection of flow.
 9. Device for mixing a hot core stream flow and acold bypass flow in a jet engine with said flows initially being guidedseparately from one another, comprising a mixing tube which encloses thehot core stream flow with the cold bypass flow flowing along an outersurface of the mixing tube, wherein the mixing tube has a truncated coneshape narrowing in a direction of the flows, wherein the mixing tube hasopenings arranged at a downstream end portion thereof for accommodatingflow of at least a portion of the hot core stream flow into the coldbypass flow, and wherein the openings have a hole collar on the outersurface of the mixing tube.
 10. Device according to claim 9, wherein theopenings have a passage area of elliptical shape with a major axis and aminor axis, and wherein the major axis of the passage area runs on theouter surface of the mixing tube in the direction of the flows and theminor axis of the passage area runs perpendicularly thereto.
 11. Deviceaccording to claim 10, wherein a height of the hole collar with respectto the outer surface of the mixing tube varies in such a way that amaximum height of the hole collar is located at an upstream apex of themajor axis of the elliptical passage area and decreases from there inthe direction of the flow.
 12. Device according to claim 10, wherein atransition from the outer surface of the mixing tube to the hole collaris of concave design.
 13. Device according to claim 9, wherein atransition from the outer surface of the mixing tube to the hole collaris of concave design.